Storage element and memory

ABSTRACT

A storage element includes a storage layer, a fixed magnetization layer, a spin barrier layer, and a spin absorption layer. The storage layer stores information based on a magnetization state of a magnetic material. The fixed magnetization layer is provided for the storage layer through a tunnel insulating layer. The spin barrier layer suppresses diffusion of spin-polarized electrons and is provided on the side of the storage layer opposite the fixed magnetization layer. The spin absorption layer is formed of a nonmagnetic metal layer causing spin pumping and provided on the side of the spin barrier layer opposite the storage layer. A direction of magnetization in the storage layer is changed by passing current in a layering direction to inject spin-polarized electrons so that information is recorded in the storage layer and the spin barrier layer includes at least a material selected from oxides, nitrides, and fluorides.

CROSS-REFERENCES TO RELATED APPLICATIONS

The present application is a continuation of U.S. application Ser. No.16/156,736, filed on Oct. 10, 2018, which us a continuation of U.S.application Ser. No. 15/667,750, filed on Aug. 3, 2017, which is acontinuation of U.S. application Ser. No. 14/882,637, filed on Oct. 14,2015, which is a continuation of U.S. application Ser. No. 14/288,005,filed on May 27, 2014, which is a continuation of U.S. application Ser.No. 11/874,045, filed on Oct. 17, 2007, now abandoned, which claimspriority to Japanese Patent Application JP 2006-335016, filed in theJapanese Patent Office on Dec. 12, 2006, the entire contents of each ofwhich are hereby incorporated by reference herein.

BACKGROUND

The present application relates to a storage element including a storagelayer, in which a magnetization state of a ferromagnetic layer is storedas information, and a fixed magnetization layer, a magnetizationdirection of which is fixed, where the magnetization direction of thestorage layer can be changed by applying a current in the directionperpendicular to the plane of the film to inject spin-polarizedelectrons. The present application also relates to a memory includingsuch storage element, and can be favorably applied to a nonvolatilememory.

High-speed, high-density DRAM is widely used as random access memory incomputers and other information devices.

However, because DRAM is volatile memory, the information within whichdisappears when power is turned off. Hence, there is a demand fornonvolatile memory in which information may not disappear when there isno power.

As such a nonvolatile memory, magnetic random access memory (MRAM), inwhich information is recorded using magnetization in a magneticmaterial, is attracting attention and is currently under development.

In MRAM, currents flow through two types of substantially perpendicularaddress lines (word lines and bit lines), and information is recorded byinverting magnetization in a magnetic layer of a magnetic storageelement at an intersection of the address lines using an electriccurrent-induced magnetic field generated by the address lines. Wheninformation is read, magnetoresistive effect (MR effect) is used, inwhich the resistance changes according to the direction of magnetizationin the storage layer of the magnetic storage element.

FIG. 1 shows a schematic (perspective) view of a typical MRAM device.

Drain regions 108, source regions 107, and gate electrodes 101, formingselection transistors to select memory cells, are formed in portionsseparated by element separation layers 102 in a silicon substrate orother semiconductor substrate 110. Above the gate electrodes 101 areprovided word lines 105 extending in the front-back direction in thefigure.

The drain regions 108 are formed so as to be shared by selectiontransistors on the left and right in the figure. Lines 109 are connectedto the drain regions 108.

Between the word lines 105 and the bit lines 106, which are positionedabove the word lines 105 and extend in the left-right direction in thefigure, are positioned magnetic storage elements 103 having a magneticlayer the magnetization direction of which is inverted. These magneticstorage elements 103 include, for example, magnetic tunnel junction(MTJ) elements. Further, the magnetic storage elements 103 areelectrically connected to the source regions 107 throughhorizontal-direction bypass lines 111 and a contact layer 104 in thevertical direction. By passing currents through a word line 105 and abit line 106, a current-induced magnetic field is applied to a magneticstorage element 103, thereby inverting the direction of magnetization inthe storage layer of the magnetic storage element 103 and informationcan be recorded.

In MRAM and other magnetic memories, in order to store recordedinformation stably, the magnetic layer (storage layer) in whichinformation is recorded may need to have a constant coercive force. Onthe other hand, in order to overwrite recorded information, a certainamount of electric current may need to pass through address lines.However, since elements forming MRAM are made finer, address lines alsogrow narrower, so that it is difficult to pass a sufficiently largecurrent.

Hence, in order to invert magnetization using small currents, memoryconfigured to use magnetization inversion caused by spin injection hasbeen attracting attention (see, for example, Japanese Unexamined PatentApplication Publication No. 2003-17782). Magnetization inversion causedby spin injection involves injecting spin-polarized electrons passedthrough a magnetic material into another magnetic material, resulting intorque generated on the other magnetic material and causing themagnetization inversion.

For example, by passing current in the direction perpendicular to theplane of a film of a giant magnetoresistive effect (GMR) element or amagnetic tunnel junction (MTJ) element, the direction of magnetizationin at least part of the magnetic layers of these elements can beinverted.

Moreover, magnetization inversion by spin injection has such anadvantage that the magnetization inversion is effected withoutincreasing the current, even if the element is very small.

FIGS. 2 and 3 are schematic views of memory configured to use themagnetization inversion caused by spin injection as described above.FIG. 2 is a perspective view, and FIG. 3 is a cross-sectional view.

Drain regions 58, source regions 57, and gate electrodes 51, formingselection transistors used to select memory cells, are each formed inportions separated by an element separation layer 52 of a siliconsubstrate or other semiconductor substrate 60. The gate electrodes 51also serve as word lines extending in the front-back direction in FIG.2.

The drain regions 58 are formed so as to be shared by selectiontransistors on the right and left in FIG. 2. Lines 59 are connected tothese drain regions 58.

Further, storage elements 53, having a storage layer the magnetizationdirection of which is inverted by spin injection, are positioned betweenthe source regions 57, and the bit lines 56 positioned above the sourceregions 57 and extending in the right-left direction in FIG. 2.

Such a storage element 53 includes, for example, a magnetic tunneljunction (MTJ) element. As shown in the figure, magnetic layers 61 and62 are provided. One of the magnetic layers 61 and 62 is a fixedmagnetization layer the magnetization direction of which is fixed, andthe other magnetic layer is a free magnetization layer, that is, astorage layer, the magnetization direction of which changes.

The storage element 53 is connected to a bit line 56 and a source region57 through a vertical contact layer 54. Accordingly, current is passedthrough the storage element 53 to cause inversion of the direction ofmagnetization in the storage layer by spin injection.

Memory configured to use magnetization inversion caused by spininjection has the feature of enabling the device structure to besimplified compared with typical MRAM shown in FIG. 1.

Further, when using magnetization inversion caused by spin injection,there is the advantage that the write current is not increased, evenwhen the element size is reduced, compared with typical MRAM in whichmagnetization inversion is effected by an external magnetic field.

In the case of MRAM, write lines (word lines and bit lines) are providedseparately from the storage elements, and by passing a current throughthe write lines to generate a current-induced magnetic field,information is written (recorded). Accordingly, a sufficiently largecurrent for writing may be passed through the write lines.

On the other hand, in memory configured to use magnetization inversioncaused by spin injection, spin injection may need to be carried out bypassing a current through storage elements to invert the direction ofmagnetization in the storage layer.

Because information is written (recorded) by directly passing a currentthrough storage elements as described above, storage elements areconnected to selection transistors so that memory cells for writing canbe selected. Here, the current flowing through a storage element islimited to the current which can be passed through a selectiontransistor (saturation current of the selection transistor).

Accordingly, information may need to be written using a current equal toor less than the saturation current of selection transistors. Therefore,the efficiency of spin injection may need to be improved so that currentpassed through storage elements may be reduced.

Further, in order to obtain a large read signal, a largemagnetoresistive change rate may need to be secured. Hence, it iseffective to provide a storage element in which a tunnel insulatinglayer (tunnel barrier layer) serves as an intermediate layer in contactwith both sides of the storage layer.

When using a tunnel insulating layer as an intermediate layer asdescribed above, an amount of current passed through the storage elementmay need to be limited to prevent dielectric breakdown of the tunnelinsulating layer. In light of this also, the current during spininjection may need to be controlled.

Hence, storage elements configured to invert the magnetization directionof the storage layer by spin injection may need to improve the spininjection efficiency and reduce the current required.

SUMMARY

When the direction of magnetization in a ferromagnetic material changeswith time, an action to impede the change may act on the magnetizationof the ferromagnetic material.

The magnitude of this action is expressed by the Gilbert dampingconstant.

When the magnetization direction in a storage layer is inverted by spininjection, a large torque exceeding such action may need to be appliedto the storage layer.

That is, when the Gilbert damping constant is large, a correspondinglylarge current may need to pass through the storage layer.

However, the ferromagnetic material alone may not determine the Gilbertdamping constant, but the value may increase depending on conditions ofadjacent layers.

When a current passes through a metal layer adjacent to theferromagnetic material, and when magnetization of the ferromagneticmaterial is in motion, a spin current flows in the adjacent metal layer.

When the spin current disappears by spin diffusion in the metal layer,magnetization movement in the ferromagnetic material is suppressed inreaction, that is, the Gilbert damping constant increases.

This phenomenon is referred to as spin pumping.

The spin pumping phenomenon has been experimentally corroborated indetail in, for example, Phys. Rev. B, 66, 104413 (2002), and in Jpn. J.Appl. Phys., 40, 580 (2001).

Thus in storage elements in which the magnetization direction isinverted through spin injection, the Gilbert damping constant mayincrease depending on metal layers adjacent to a storage layer and, as aresult, the current necessary for magnetization inversion (the inversioncurrent) may increase.

Further, it is desirable that the element size of storage layers andsaturation magnetization thereof be decreased as much as possible toreduce the inversion current.

However, if element size and saturation magnetization of the storagelayer are small, thermal stability of the storage element is reduced,and operation may become unstable.

It is desirable to provide a storage element having sufficient thermalstability, and in which the occurrence of the spin pumping can besuppressed, as well as a memory having such storage elements.

According to an embodiment, there is provided a storage elementincluding a storage layer, a fixed magnetization layer, a spin barrierlayer, and a spin absorption layer. The storage layer stores informationbased on a magnetization state of a magnetic material. The fixedmagnetization layer is provided for the storage layer with a tunnelinsulating layer in between. The spin barrier layer suppresses diffusionof spin-polarized electrons and is provided on the side of the storagelayer opposite the fixed magnetization layer. The spin absorption layerincludes a nonmagnetic metal layer causing the spin pumping phenomenonand is provided on the side of the spin barrier layer opposite thestorage layer. A direction of magnetization in the storage layer ischanged by passing current in a layering direction to injectspin-polarized electrons so that information is recorded in the storagelayer. The spin barrier layer includes at least one material selectedfrom oxides, nitrides, and fluorides.

According to an embodiment, there is provided a memory including astorage element having a storage layer which stores information based ona magnetization state of a magnetic material, and two types of linewhich mutually intersect. The storage element has the configuration ofthe above-described storage element according to an embodiment. Thestorage elements are positioned in proximity to intersections of the twotypes of line, positioned between the two types of line. An electriccurrent flows in the storage elements through the two types of line in alayering direction, and spin-polarized electrons are injected.

The storage element according to an embodiment has a storage layer whichstores information based on the state of magnetization of a magneticmaterial. A fixed magnetization layer is provided for the storage layerwith a tunnel insulating layer in between. A direction of magnetizationin the storage layer is changed by passing a current in a layeringdirection to inject spin-polarized electrons so that information isrecorded in the storage layer. Accordingly, information can be recordedby passing a current in the layering direction and injectingspin-polarized electrons.

Further, a spin barrier layer which suppresses the spin pumpingphenomenon is provided on the side of the storage layer opposite thefixed magnetization layer and includes one or more materials selectedfrom oxides, nitrides, and fluorides so that the spin barrier layer maysuppress occurrence of the spin pumping phenomenon. Accordingly, thecurrent for inverting the magnetization of the storage layer can bereduced, and the efficiency of spin injection can be improved. Further,the thermal stability of the storage layer can be improved by providinga spin barrier layer, so that information recorded in the storage layercan be stored with stability. Further, since a spin absorption layerformed of a nonmagnetic metal layer causing the spin pumping phenomenonis provided on the side of the spin barrier layer opposite the storagelayer, the current for inverting the magnetization of the storage layercan be further reduced compared with a configuration provided with aspin barrier layer alone, so that the spin injection efficiency can beimproved.

The memory according to an embodiment has storage elements, having astorage layer which stores information based on the magnetization stateof a magnetic material, and two types of line which mutually intersect.The storage elements have the configuration of the above-describedstorage element according to an embodiment. The storage elements arepositioned in proximity to the intersections of the two types of line,positioned between the two types of line. An electric current flows inthe storage elements through the two types of line in the layeringdirection, and spin-polarized electrons are injected, so that currentflows through the two types of line in the layering direction of thestorage elements, and information can be recorded through spininjection.

With spin injection, an amount of current for inverting themagnetization direction of the storage element (threshold current) canbe reduced.

Further, information recorded in the storage layer of a storage elementcan be stored with stability.

According to an embodiment, spin injection efficiency can be improved,so that the current amount necessary for information recording can bereduced.

As a result, power consumption for the memory as a whole can be reduced.

Hence, it is possible to obtain a memory with lower power consumptionthan a typical memory in the past.

Further, because the storage layer in storage elements has sufficientthermal stability, the storage elements have excellent informationretention characteristics.

Moreover, since the current amount necessary for information recordingcan be reduced, the operating region for passing a current and recordinginformation can be expanded, and a large operating margin can besecured. Hence, a memory which operates with stability and is highlyreliable can be obtained.

Additional features and advantages are described herein, and will beapparent from, the following Detailed Description and the figures.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a perspective view schematically showing a configuration of aMRAM of the related art.

FIG. 2 is a schematic (perspective) view showing a configuration of amemory using magnetization inversion through spin injection.

FIG. 3 is a cross-sectional view of the memory in FIG. 2.

FIG. 4 is a schematic (perspective) view showing a configuration of amemory according to an embodiment.

FIG. 5 is a cross-sectional view of a storage element in FIG. 4.

FIG. 6 is a schematic view showing a configuration of a storage elementrepresenting a comparative example.

FIG. 7 is a schematic view showing a configuration of a storage elementrepresenting another comparative example.

FIG. 8 is a schematic view showing a configuration of a storage elementrepresenting still another comparative example.

FIG. 9 shows a method of measuring the inversion current Ic0 and anindex Δ of thermal stability.

DETAILED DESCRIPTION

According to an embodiment, a magnetization direction in a storage layerof a storage element is inverted by the above-described spin injectionso that information is recorded. The storage layer includes aferromagnetic layer or other magnetic material, and stores informationbased on a magnetization state (magnetization direction) of the magneticmaterial.

In a basic operation to invert the magnetization direction in a magneticlayer through spin injection, a current, equal to or greater than acertain threshold, is passed through a storage element formed of a giantmagnetoresistive effect (GMR) element or a magnetic tunnel junction(MTJ) element, in the direction perpendicular to the plane of a film. Atthis time, the polarity (direction) of the current depends on thedirection of the magnetization inverted.

If a current of absolute value smaller than the threshold is passed,magnetization inversion may not occur.

According to an embodiment, in consideration of the saturation currentvalue of selection transistors as described above, a magnetic tunneljunction (MTJ) element using a tunnel insulating layer formed of aninsulator is formed as a nonmagnetic intermediate layer between thestorage layer and a fixed magnetization layer.

By forming the magnetic tunnel junction (MTJ) element using the tunnelinsulating layer, the magnetoresistive change rate (MR ratio) can belarge and the read signal intensity can be increased, compared with thecase where a giant magnetoresistive effect (GMR) element is formed usinga nonmagnetic conducting layer.

When spin injection is used to invert the direction of magnetization inthe magnetic layer, the current required is characterized by formula [1]below (see, for example, F. J. Albert et al, Appl. Phys. Lett., 77, p.3809, 2000, and similar).

$\begin{matrix}{{\frac{\eta\; I_{c\; 0}\tau_{1}}{e} = \frac{M_{s}V}{\mu_{B}}}{\tau_{1} = {{1/\alpha}\mspace{11mu}{\gamma\left( {H_{c} + {\frac{1}{2}\; H_{d}}} \right)}}}} & {{Formula}\mspace{14mu}\lbrack 1\rbrack}\end{matrix}$

In formula [1], Ic0 is equivalent to the current value for themagnetization in the magnetic layer at absolute zero temperature tobegin precessional motion caused by spin injection. The valuedetermines, in relative terms, the actual magnitude of the inversioncurrent.

In order to secure a broad operating margin for the storage element andinduce stable operation of the storage element, the Ic0 may need to besmall.

With small Ic0, power consumption of storage elements, and of the memoryas a whole, can be reduced.

Further, with small Ic0, it becomes possible to use selectiontransistors with low saturation current values, that is, with small gatewidths, so that memory cells can be made small, and memories can furtherbe integrated. Accordingly, the memories can be reduced in size, andstorage capacities can be increased.

In the above-described formula [1], the Gilbert damping constant α andIc0 are in a proportional relationship.

That is, when the Gilbert damping constant α is increased by theabove-described spin pumping phenomenon, Ic0 increases simultaneously.

Because the above-described fact may be against efforts to secure abroad operating margin, it is essential that the spin pumping phenomenonbe controlled in actual storage elements so that an increase in Ic0 maynot occur. Referring to formula [1], Ic0 may be reduced by lowering thesaturation magnetization Ms and volume V of the storage layer.

In order to store information recorded in a storage element, the index(parameter) Δ for the thermal stability of the storage layer may need tobe maintained at or above a certain constant value. In general, it ispreferable that the index Δ of thermal stability be 60 or higher, andmore preferably 70 or higher.

The index Δ of thermal stability is expressed by the following equation.Δ=Ms·V·Hc·(½kT)  (1)

Here k is the Boltzmann constant and T is the temperature.

As seen from the above equation (1), if the saturation magnetization Msand volume V are reduced, the thermal stability index Δ falls.

Thus there is a trade-off between decreases in Ic0 and increases in Δ,and so the storage element may need to be configured so as to satisfythe requirements of both sides.

When a storage element is formed using an MTJ element, a GMR element, oranother magnetoresistive effect element, typically an electrode layer orother nonmagnetic metal layer is connected on the side of the storagelayer opposite the fixed magnetization layer, in order to pass currentthrough the storage element.

Such nonmagnetic metal layers may be, for example, a lower electrodelayer, upper electrode layer, metal underlayer, a cap layer, and thelike.

If such a nonmagnetic metal layer is directly connected with the storagelayer, constituent elements of the nonmagnetic metal layer diffuse intothe ferromagnetic material of the storage layer by diffusion at theinterface. Then, a characteristic-degraded region, in which normalcharacteristics of the ferromagnetic material of the storage layer aredegraded, may be formed. In particular, the above-described lowerelectrode layer, upper electrode layer, metal underlayer, cap layer, andthe like are formed to be thick (having the film thickness two toseveral times greater) compared with the storage layer, so that a largequantity of nonmagnetic metal elements may be diffused.

When such characteristic-degraded region occurs in the storage layer,the characteristics of the storage layer as a magnetic material areimpaired, and the MR ratio, Ms, and the like are degraded.

When the MR ratio, Ms value and the like are degraded in this way, itmay be difficult to read information recorded to the storage element, orthe thermal stability index Δ of the storage layer may be lowered, sothat the storage element becomes thermally unstable, which isundesirable for the storage element.

Hence, it is desirable that there may be no characteristic-degradedregion occurred within the storage layer due to diffusion between thestorage layer and the nonmagnetic metal layer.

As a result of various studies, expected characteristics of theferromagnetic material of the storage layer have been obtained asdescribed below. Specifically, if a spin barrier layer to suppressdiffusion of spin-polarized electrons is provided on the side of thestorage layer opposite the fixed magnetization layer and separates thestorage layer and the nonmagnetic metal layer, the above-described spinpumping phenomenon may be suppressed. Accordingly, the spin injectionefficiency may be improved. In addition, occurrence of theabove-described characteristic-degraded region can be suppressed.

Further, Ic0 may be further reduced by providing a spin absorption layerformed of a nonmagnetic metal layer which causes the spin pumpingphenomenon on the side of the spin barrier layer opposite the storagelayer.

Hence according to an embodiment, a storage element is configured byproviding a spin barrier layer to suppress diffusion of spin-polarizedelectrons on the side of the storage layer opposite the fixedmagnetization layer. Further, the storage element includes a spinabsorption layer formed of a nonmagnetic metal layer which causes thespin pumping phenomenon provided on the side of the spin barrier layeropposite the storage layer.

Further, according to an embodiment, the spin barrier layer includes oneor more materials selected from oxides, nitrides, and fluorides.

That is, the spin barrier layer includes one or more types of materialselected from oxides, nitrides, and fluorides, or includes one or moretypes of material selected from oxides, nitrides, and fluorides as themain component with small amounts of other elements (for example, metalelements or the like) added.

By thus forming the spin barrier layer from one or more types ofmaterial selected from oxides, nitrides, and fluorides, a spin barrierlayer is essentially insulated.

Specifically, for example, magnesium oxide, aluminum oxide, aluminumnitride, and other compounds using elements such as magnesium andaluminum which have a strong affinity for oxygen and nitrogen, can beused.

Apart from these, various other materials such as SiO₂, Bi₂O₃, MgF₂,ZnO, Ta₂O₅, CaF, SrTiO₂, AlLaO₃, Al—N—O, and the like, can also be used.

The spin barrier layer may also be formed using the same material as thetunnel insulating layer between the storage layer and the fixedmagnetization layer.

If the spin barrier layer, which suppresses diffusion of spin-polarizedelectrons, is thus provided to be in contact with the storage layer onthe side opposite the fixed magnetization layer, the above-describedspin pumping phenomenon may be suppressed, and the spin injectionefficiency may be improved.

Further, since occurrence of a characteristic-degraded region due todiffusion between the storage layer and the nonmagnetic metal layer canbe suppressed by the spin barrier layer which is basically insulating,expected characteristics of the ferromagnetic material of the storagelayer can be obtained.

Accordingly, degradation of MR ratio due to the characteristic-degradedregion can be suppressed, and the read output can be improved. As aresult, for example, a thin storage layer to indicate a relative maximumspin injection efficiency can be designed. In other words, the spininjection efficiency can be improved and Ic0 can be reduced without theMR ratio or other characteristics being degraded.

Further, because occurrence of a characteristic-degraded region can besuppressed, the thickness of the storage layer can be reduced to thatextent.

Since magnesium oxide (MgO) is in particular used as the material of thetunnel insulating layer, the magnetoresistive change rate (MR ratio) canbe made larger than in cases where aluminum oxide has been typicallyemployed.

In general, the spin injection efficiency depends on the MR ratio, andthe higher the MR ratio, the more the spin injection efficiency η isimproved, so that the magnetization inversion current density can bereduced.

Hence, when magnesium oxide is used as the material of the tunnelinsulating layer constituting an intermediate layer, the write thresholdcurrent caused by spin injection can be lowered, and information can bewritten (recorded) using a small current. Further, the read signalintensity can be increased.

Accordingly, a sufficient MR ratio (TMR ratio) can be secured, so thatthe write threshold current by spin injection can be lowered, andinformation can be written (recorded) using a small current. Further,the read signal intensity can be increased.

When the tunnel insulating layer is formed of a magnesium oxide (MgO)film, it is desirable that the MgO film be crystallized, and that thecrystal orientation be maintained in the 001 direction.

When magnesium oxide is used as the tunnel insulating layer, typically ahigh annealing temperature of 300° C. or higher, and more desirably 340°C. to 380° C., may be used to obtain excellent MR characteristics. Suchtemperature is higher than the range of annealing temperatures (250 to280° C.) used in the case of the aluminum oxide which has been used asan intermediate layer in the related art.

This is because a high temperature may be necessary to form magnesiumoxide with an appropriate internal structure and crystal structure.

If a ferromagnetic material without heat resistance to high-temperatureannealing is used as the ferromagnetic layer of the storage element,excellent MR characteristics may not be obtained. However, according toan embodiment, since diffusion into the ferromagnetic layer which formsthe storage layer is suppressed by providing a spin barrier layer, heatresistance of the storage layer is improved. Accordingly, magneticcharacteristics of the storage layer may not be deteriorated inannealing at 340° C. to 400° C.

Further, in order to pass a sufficient write current through the storageelement, a sheet resistance value of the tunnel insulating layer (tunnelbarrier layer) may need to be small.

The sheet resistance of the tunnel insulating layer may need to be keptto several tens of Ω-μm2 or lower, in view of obtaining the currentdensity to invert the magnetization direction in the storage layer byspin injection.

In the case of a tunnel insulating layer formed of an MgO film, thethickness thereof may need to be 1.5 nm or less in order that the sheetresistance be in the above-described range.

In addition to magnesium oxide, other materials such as aluminum oxide,aluminum nitride, SiO₂, Bi₂O₃, MgF₂, CaF, SrTiO₂, AlLaO₃, Al—N—O, andvarious other insulators, dielectrics, and semiconductors can be used asthe material of the tunnel insulating layer between the storage layerand the fixed magnetization layer.

Further, it is desirable that the storage element be made small so thatthe magnetization direction in the storage layer can be inverted easilyby a small current. It is preferable that the area of the storageelement be 0.04 μm2 or less.

The storage layer typically includes more than one layer mainly formedof such ferromagnetic materials as Co, Fe and Ni, each layer includingan alloy of two or more types of material. The storage layer is formedof such layers stacked.

Alloy elements are added to each of the ferromagnetic layers to controlthe saturation magnetization and other magnetic characteristics as wellas the crystal structure (crystalline structure, microcrystal structure,amorphous structure). For example, with a CoFe alloy, CoFeB alloy, Fealloy, or NiFe alloy as the main component, Gd or another magneticelement, or, as other elements, one or a plurality of types among B, C,N, Si, P, Al, Ta, Mo, Cr, Nb, Cu, Zr, W, V, Hf, Gd, Mn, and Pd can beadded. Also, amorphous material obtained by adding one or more elementsselected from Zr, Hf, Nb, Ta, and Ti to Co, or Heusler materials such asCoMnSi, CoMnAl, CoCrFeAl, or the like can be used.

When using CoFeB alloy for the ferromagnetic layer forming the storagelayer, it is preferable that the total content ratio of the Co and Fewhich are ferromagnetic components of the storage layer be 60 atom % orhigher, in view of securing sufficient magnetization and soft magneticcharacteristics.

If the total content ratio of Co and Fe is 60 atom % or less, sufficientsaturation magnetization and coercive force as a ferromagnetic layer maynot be obtained. Further, when the Co:Fe ratio is in the range of 90:10to 40:60, typically the magnetic anisotropy dispersion is appropriatelysuppressed, and satisfactory soft magnetic characteristics are obtained.

A plurality of materials or a plurality of ferromagnetic layers indifferent composition ranges can be directly layered to form the storagelayer as well. Ferromagnetic layers and soft magnetic layers can belayered, or a plurality of ferromagnetic layers can be layered throughsoft magnetic layers. The advantageous results according to anembodiment may be obtained when such layering is used.

Further, according to an embodiment, if two or more ferromagnetic layersare stacked through nonmagnetic layers to form the storage layer, thesaturation magnetization Ms of the storage layer can be lowered, therebylowering the current threshold Ic0.

It is preferable that Ti, Ta, Nb, or Cr be used as the nonmagnetic layermaterial, where these elements may be used alone, or in an alloy.

If similar advantageous results can be obtained, other nonmagneticelements may be used. For example, Ru, Os, Re, Ir, Au, Ag, Cu, Al, Bi,Si, B, C, Pd, Pt, Zr, Hf, W, Mo, and the like may be used.

For example, when the main component of the ferromagnetic layers of thestorage layer is CoFeB and the nonmagnetic layers use one or morenonmagnetic elements selected from Ti, Ta, Nb, and Cr, it is preferablethat the thickness of the nonmagnetic layer be determined such that thecontent of nonmagnetic elements in the entire storage layer be 1 atom %or higher and 20 atom % or lower.

If the content is low (if the nonmagnetic layers are thin), then theeffect in reducing the saturation magnetization is decreased, and it isdifficult to deposit ferromagnetic layers on top of nonmagnetic layersin a satisfactory state.

If the content is high (if the nonmagnetic layers are thick), then thesaturation magnetization is reduced, but the storage element MR ratio isalso reduced, so that reading becomes difficult.

In those cases, nonmagnetic elements are included in the storage layermainly for the purpose of lowering the saturation magnetization Ms ofthe storage layer. However, oxides such as MgO, Ta₂O₃, and Al₂O₃ canalso be inserted into the layered structure of the storage layer so asto improve the thermal stability index 4.

At this time, it is desirable that the thicknesses of the respectiveoxide layers be 0.5 nm or less so that resistance value of the storagelayer may not become large.

It should be appreciated that nonmagnetic elements to lower thesaturation magnetization Ms and oxides to improve the thermal stabilityindex Δ can be added simultaneously.

Instead of stacking two or more ferromagnetic layers through nonmagneticlayers, nonmagnetic elements may be included in the ferromagneticmaterial of the storage layer. With such a configuration, the saturationmagnetization Ms of the storage layer can be similarly reduced, andconsequently the current threshold Ic0 can be lowered.

A storage layer with such configuration can be formed by, for example,using a target containing a ferromagnetic material and a nonmagneticelement, or by co-sputtering where a nonmagnetic element is mixed intothe ferromagnetic material.

In these cases, the content of the nonmagnetic element is determined ina manner similar to the case of layered configuration.

When a nonmagnetic element is included in the ferromagnetic material ofthe storage layer, the nonmagnetic element is also distributed in thevicinity of the interface between the tunnel insulating layer and thestorage layer, which may lower the MR ratio.

In other words, from the standpoint of the MR ratio, if the content isthe same, a structure in which ferromagnetic layers and nonmagneticlayers are layered is advantageous.

A nonmagnetic metal material is used for the spin absorption layerprovided on the side of the spin barrier layer opposite the storagelayer.

According to an embodiment, the spin absorption layer is formed using amaterial selected such that, if the spin absorption layer were providedin direct contact with the storage layer, the spin pumping phenomenonwould cause the Gilbert damping constant of the storage layer to beincreased.

If the spin absorption layer is in direct contact with the storagelayer, the spin pumping phenomenon occurs, but when a spin barrier layerof MgO or another material separates the spin absorption layer from thestorage layer, the spin pumping phenomenon may not occur, and inaddition, although the reason is not clear, the Ic0 is reduced comparedwith a case in which no spin absorption layer is provided.

Pt, Pd, Ru and Au may represent such materials selected and used but anymaterial may be used as long as a similar effect is obtained. Theabove-described materials have short spin diffusion lengths, andmaterials with similarly short spin diffusion lengths can be used.

It is preferable that the thickness of the spin absorption layer begreater than the spin diffusion length of the material forming the spinabsorption layer. If the thickness of the spin absorption layer isshorter than the spin diffusion length, then the spin is notsufficiently absorbed, and so the effect of providing the spinabsorption layer is reduced.

According to an embodiment, it is desirable that a storage elementshould include the fixed magnetization layer having a unidirectionalanisotropy, and it is desirable that the storage layer have a uniaxialanisotropy.

Further, it is preferable that the film thicknesses of the fixedmagnetization layer and of the storage layer be 1 nm to 40 nm and 1 nmto 10 nm, respectively.

The other configuration of the storage element can be similar to theconfiguration of storage elements of the related art which recordinformation through spin injection.

The fixed magnetization layer fixes the direction of the magnetizationusing a ferromagnetic layer alone, or using the antiferromagneticcoupling between an antiferromagnetic layer and a ferromagnetic layer.

The fixed magnetization layer has a single ferromagnetic layer, or has alayered ferrimagnetic structure in which a plurality of ferromagneticlayers are layered with nonmagnetic layers in between. When the fixedmagnetization layer has a layered ferrimagnetic structure, thesensitivity to external magnetic fields of the fixed magnetization layercan be reduced, and so magnetization fluctuation in the fixedmagnetization layer due to external magnetic fields can be controlled tostably operate the storage element. Further, the film thicknesses of therespective ferromagnetic layers can be adjusted, so that leakagemagnetic fields from the fixed magnetization layer can be reduced.

Co, CoFe, CoFeB, and the like can be used as materials of theferromagnetic layers in a fixed magnetization layer with a layeredferrimagnetic structure. Ru, Re, Ir, Os, and the like can be used asnonmagnetic layer materials.

FeMn alloy, PtMn alloy, PtCrMn alloy, NiMn alloy, IrMn alloy, NiO,Fe₂O₃, and other magnetic materials can be used as antiferromagneticlayer materials.

Ag, Cu, Au, Al, Si, Bi, Ta, B, C, O, N, Pd, Pt, Zr, Hf, Ir, W, Mo, Nb,and other nonmagnetic elements can be added to these magnetic materialsto adjust the magnetic characteristics, and to adjust the crystalstructure, crystallinity, stability of physical properties, and variousother physical properties.

The storage element has a structure in which the storage layer may bepositioned above or below the fixed magnetization layer.

As a method for reading information recorded in the storage layer of thestorage element, a magnetic layer serving as information reference maybe provided to the storage layer of the storage element through a thininsulating film, and information may be read by passing a ferromagnetictunnel current flowing through the insulating layer. Alternatively,information may be read using a magnetoresistance effect.

Next, specific embodiments are described.

FIG. 4 shows a schematic (perspective) view of a memory according to anembodiment.

The memory includes storage elements capable of storing informationbased on magnetization states and arranged in the vicinity ofintersections of two types of address line (for example, word lines andbit lines) which intersect perpendicularly.

Specifically, drain regions 8, source regions 7, and gate electrodes 1,forming selection transistors used to select memory cells, are formed inportions separated by element separation layers 2 on a silicon substrateor other semiconductor substrate 10. The gate electrodes 1 also serve asaddress lines (for example, word lines) extending in the front-backdirection in the figure. The drain regions 8 are formed to be common toselection transistors on the left and right in the figure; to thesedrain regions 8 are connected lines 9.

Storage elements 3 are positioned between the source regions 7, and theother address lines (for example, bit lines) 6 extending above in theright-left direction in the figure. These storage elements 3 have astorage layer formed of a ferromagnetic layer the magnetizationdirection of which is inverted by spin injection.

The storage element 3 is positioned in the vicinity of the intersectionof the two types of address line 1 and 6.

In the storage element 3, the bit line 6 and source region 7 areconnected through a vertical contact layer 4.

Accordingly, a current can be passed in the vertical direction in thestorage element 3 through the two types of address line 1 and 6, and sothe magnetization direction in the storage layer can be inverted by spininjection.

FIG. 5 is a cross-sectional view of the storage element 3 in the memoryof this embodiment.

As shown in FIG. 5, the storage element 3 includes a fixed magnetizationlayer 31 below the storage layer 32, which includes a ferromagneticlayer 17 the direction of magnetization M1 of which is inverted by spininjection.

Between the storage layer 32 and the fixed magnetization layer 31 isprovided an insulating layer 16 which serves as a tunnel barrier layer(tunnel insulating layer). An MTJ element is formed by the storage layer32 and the fixed magnetization layer 31.

Below the fixed magnetization layer 31 is formed an underlayer 11, and acap layer 20 is formed as the uppermost layer.

Further, the fixed magnetization layer 31 has an exchange-bias layeredferrimagnetic structure.

Specifically, two ferromagnetic layers 13 and 15 are layered andantiferromagnetically coupled with a nonmagnetic layer 14 in between,and an antiferromagnetic layer 12 is positioned below and adjacent tothe ferromagnetic layer 13, to form the fixed magnetization layer 31.The direction of the magnetization M13 of the ferromagnetic layer 13 isfixed by the antiferromagnetic layer 12.

With the antiferromagnetic coupling of the two ferromagnetic layers 13and 15, the magnetization M13 of the ferromagnetic layer 13 is directedrightward, and the magnetization M15 of the ferromagnetic layer 15 isdirected leftward, and the two are directed in opposite directions.

As a result, the leakage magnetic flux from the ferromagnetic layer 13and the leakage magnetic flux from the ferromagnetic layer 15 canceleach other in the fixed magnetization layer 31.

Alloy materials including one type, or two or more types selected fromiron, nickel, and cobalt can be used as the material of theferromagnetic layer 17 that is the storage layer 32, although there isno particular limitations. In addition, transition metal elements suchas Nb, Zr, Gd, Ta, Ti, Mo, Mn, Cu and the like, as well as lightelements such as Si, B, and C, may be included. Also, the storage layer32 may be formed by directly stacking a plurality of films of differentmaterials, such as a layered film of CoFeB/Ta/CoFeB.

Alloy materials including one type, or two or more types selected fromiron, nickel, and cobalt can be used as the material of theferromagnetic layers 13 and 15 in the fixed magnetization layer 31,although there is no particular limitations. In addition, transitionmetal elements such as Nb, Zr, Gd, Ta, Ti, Mo, Mn, Cu and the like, aswell as light elements such as Si, B, and C, may be included. Also, theferromagnetic layers 13 and 15 may be formed by directly (without anynonmagnetic layer in between) stacking a plurality of films of differentmaterials, such as layered films of CoFe/NiFe/CoFe.

Ruthenium, copper, chromium, gold, silver, or the like can be used asthe material of the nonmagnetic layer 14 forming the layeredferrimagnetic structure of the fixed magnetization layer 31.

The film thickness of the nonmagnetic layer 14 may differ depending onthe material, but it is preferable that the thickness be substantiallyin the range of 0.5 nm to 2.5 nm.

The film thicknesses of the ferromagnetic layers 13, 15 of the fixedmagnetization layer 31 and of the ferromagnetic layer 17 of the storagelayer 32 can be adjusted appropriately. It is suitable that thethicknesses be 1 nm or greater and 5 nm or less.

According to an embodiment, the storage element 3 includes in particulara spin barrier layer 18 which suppresses diffusion of spin-polarizedelectrons and is provided on the side of the storage layer 32 oppositethe fixed magnetization layer 31, that is, as the layer above thestorage layer 32. Further, the storage element 3 includes a spinabsorption layer 19 provided above the spin barrier layer.

The spin barrier layer 18 includes one or more types of materialselected from oxides, nitrides, and fluorides.

Specifically, the spin barrier layer 18 includes one or more types ofmaterial selected from oxides, nitrides, and fluorides, or includes amaterial the main component of which is one or more types of materialselected from oxides, nitrides, and fluorides, to which small amounts ofanother element (for example, a metal element, or the like) is added.

Since such spin barrier layer 18 is provided, the spin pumpingphenomenon during inversion of the direction of the magnetization M1 ofthe storage layer 32 is suppressed.

Further, diffusion of metal elements from the spin absorption layer 19or from the cap layer 20 into the storage layer 32 is suppressed.Accordingly, the characteristics which are normally expected of theferromagnetic material of the storage layer 32 can be obtained, and sothe thermal stability index Δ of the storage layer 32 can be large. As aresult, thermal stability of the storage layer 32 is improved as well.

Further, since the spin absorption layer 19 is provided between the spinbarrier layer 18 and the cap layer 20, the efficiency of spin injectionis further improved, and Ic0 can be reduced.

Also, according to an embodiment, when a magnesium oxide layer is usedas the insulating layer 16 which is an intermediate layer, themagnetoresistive change rate (MR ratio) can be increased.

By increasing the MR ratio as described above, the efficiency of spininjection is improved, and the current density to invert the directionof the magnetization M1 in the storage layer 17 can be reduced.

The storage elements 3 according to an embodiment can be manufactured byforming layers continuously from the underlayer 11 to the cap layer 20in a vacuum device, and afterward by etching and performing othertreatment to form the pattern of the storage elements 3.

According to the above-described embodiment, the spin barrier layer 18including one or more types of material selected from oxides, nitridesand fluorides is provided on the side of the storage layer 32 oppositethe fixed magnetization layer 31. Therefore, diffusion of spin-polarizedelectrons is controlled with the spin barrier layer 18. As a result,spin accumulation occurs in the storage layer 32, and the spin pumpingphenomenon is suppressed during inversion of the direction ofmagnetization M1 in the ferromagnetic layer 17 of the storage layer 32.

Hence, deterioration of the spin injection efficiency due to the spinpumping phenomenon can be prevented, and the spin injection efficiencycan be improved.

Further, since diffusion of metal elements from the cap layer 20 intothe storage layer 32 is suppressed using the spin barrier layer 18 andthe characteristics which are normally expected of the ferromagneticmaterial of the storage layer 32 can be obtained, the thermal stabilityindex Δ of the storage layer 32 can be large. As a result, thermalstability of the storage layer 32 is improved as well.

Since the thermal stability of the storage layer 32 is improved, theoperating range of the storage element 3, where a current is passed torecord information, can be expanded, a broad operating margin can besecured, and the storage element 3 can operate with stability.

Hence a highly reliable memory which operates stably can be obtained.

Further, since the spin absorption layer 19 is provided on the side ofthe spin barrier layer 18 opposite the storage layer 32, the spininjection efficiency can be further improved, and Ic0 can be lowered.

According to the storage element 3 of an embodiment, the spin injectionefficiency can be improved, so that an amount of current to invert thedirection of the magnetization M1 of the storage layer 32 by spininjection can be reduced.

Hence, the power consumption of a memory including such storage elements3 can be decreased.

When manufacturing the memory configured as shown in FIG. 4 andincluding the storage elements 3 shown in FIG. 5, there is an advantagethat processes for forming a typical semiconductor MOS can be applied.

Hence the memory of an embodiment can be used as general-use memory.

In particular, the storage element 3 shown in FIG. 5 has the spinbarrier layer 18, so that heat resistance of the storage layer 32 isimproved. Accordingly, there is no degradation of the magneticcharacteristics of the storage layer 32 upon annealing at 340° C. to400° C., and processes for forming a typical semiconductor MOS can beapplied easily.

Here, specific materials, film thicknesses, and the like were selectedfor each layer, and characteristics of a storage element having theconfiguration according to an embodiment.

As shown in FIG. 4, other semiconductor circuitry for switching and thelike are provided in addition to the storage elements in an actualmemory. Here, however, wafers on which storage elements alone werefabricated were used in studies for the purpose of obtaining themagnetization inversion characteristics of the storage layer.

EXAMPLES

A thermal oxide film of thickness 2 μm was formed on a silicon substrateof thickness 0.575 mm, and on top of this was formed a storage element 3with the configuration shown in FIG. 5.

Specifically, the materials and film thicknesses of the storage element3 configured as shown in FIG. 5 were selected for each layer as follows.Ta film 3 nm thick was selected as the underlayer 11. PtMn film 30 nmthick was selected as the antiferromagnetic layer 12. CoFe film 2.2 nmthick was selected as the ferromagnetic layer 13. CoFeB film 2 nm thickwas selected as the ferromagnetic layer 15 of the fixed magnetizationlayer 31. Ru film 0.8 nm thick was selected as the nonmagnetic layer 14of a fixed magnetization layer 31 having a layered ferrimagneticstructure. MgO film 0.8 nm thick was selected as the tunnel insulatinglayer 16. CoFeB (1 nm)/Ta (0.2 nm)/CoFeB (1 nm) layered film wasselected as the storage layer 32. MgO film 1.1 nm thick was selected asthe spin barrier layer 18. Pt or Pd film 3 nm thick was selected as thespin absorption layer 19. Ta film 5 nm thick was selected as the caplayer 20.

The storage layer 32 is a CoFeB/Ta/CoFeB layered film, differing fromthe ferromagnetic layer 17 shown in FIG. 5 having one layer. However,because the Ta film between the two CoFeB layers is 0.2 nm in thicknessthat is thin, the two CoFeB layers have magnetizations in the samedirection with no antiferromagnetic coupling. Therefore, theconfiguration can be regarded as similar to that with the ferromagneticlayer 17 shown in FIG. 5 having one layer.

In the above film configuration, the composition of the CoFeB films isCo48Fe32B20 (atom %), the composition of the CoFe film is Co90Fe10 (atom%), and the composition of the PtMn film is Pt38Mn62 (atom %).

A DC magnetron sputtering method was used to deposit each of the layersother than the tunnel insulating layer 16 and the spin barrier layer 18,which were formed from MgO.

The tunnel insulating layer 16 and spin barrier layer 18, including MgOfilm, were deposited using an RF magnetron sputtering method.

After depositing all the layers of the storage element 3, heat treatmentwas performed at 340° C. for two hours in a 10 kOe field in a heattreatment furnace with a magnetic field applied to perform ordering heattreatment of the PtMn film of the antiferromagnetic layer 12.

Next, photolithography was used to form a mask for the word lineportions, after which Ar plasma was used to perform selective etching oflayered film portions other than the word lines, to form the word lines(lower electrodes). At this time, portions other than the word lineswere etched to a substrate depth of 5 nm.

Subsequently, an electron beam drawing device was used to form the maskof a pattern of the storage elements 3, selective etching of the layeredfilm was performed, and the storage elements 3 were formed. Otherportions than the storage elements 3 were etched to an antiferromagneticfilm 12 depth of 10 nm.

An elliptical shape of minor axis length 70 nm and major axis length 250nm was formed as the pattern of the storage elements 3.

Next, portions other than the storage elements 3 were insulated bysputtering Al₂O₃ having a thickness of approximately 100 nm.

Subsequently, photolithography was used to form bit lines serving asupper electrodes and pads for measurements, to complete fabrication ofsamples of the storage elements 3.

Further, using the above-described manufacturing method, samples of thestorage elements 3 using Pt film as the spin absorption layer 19, andsamples using Pd film as the spin absorption layer 19. These were usedas samples in Example 1 and Example 2 respectively.

COMPARATIVE EXAMPLES

As Comparative Example 1, a sample of a storage element 70 wasfabricated, by a similar fabrication method, but having a configurationin which, as shown in the cross-sectional view of FIG. 6, no spinbarrier layer 18 or spin absorption layer 19 were provided for thestorage element 3 (storage layer 32/cap layer 20). As ComparativeExample 2, a sample of a storage element 80 was fabricated, by a similarfabrication method, but having a configuration in which, as shown in thecross-sectional view of FIG. 7, no spin barrier layer 18 was providedfor the storage element 3 (storage layer 32/spin absorption layer 19/caplayer 20). In Comparative Example 2, the spin absorption layer 19 was aPt film.

Further, as Comparative Example 3, a sample of a storage element 90 wasfabricated, by a similar fabrication method, but having a configurationin which, as shown in the cross-sectional view of FIG. 8, no spinabsorption layer 19 was provided for the storage element 3 (storagelayer 32/spin barrier layer 18/cap layer 20).

Measurement of Inversion Current Ic0 and Thermal Stability Index

The inversion current Ic0 and thermal stability index Δ for samples ofthe storage element according to each of the Examples and ComparativeExamples were measured as follows.

At a finite temperature, the current Ic at which magnetization inversionoccurs by spin injection is in fact different from Ic0. This is because,due to the small size of the storage element, the effects of thermalfluctuations may not be ignored.

In general, when the duration of current application is approximately100 ns or longer, Ic<Ic0 is obtained and the thermal stability index Δis determined according to the degree of Ic being smaller than Ic0.

Specifically, when the current application time dependence of Ic ismeasured and the value of Ic is plotted against the current applicationtime on a log scale, the reciprocal of the slope is the index 4. Thatis, the better the thermal stability, the more independent Ic is of thecurrent application time.

The current application time dependence of Ic was measured, and asschematically shown in FIG. 9, Ic was plotted against the currentapplication time on a log scale, and the Ic resulting when extrapolatingto a current application time of 1 ns was obtained to be Ic0. In actualmeasurements, the current application time was varied from 10 μs to 100ms, and measurements were repeated three times for the same currentapplication time. Since there might be variations of storage elements,approximately 30 storage elements were fabricated having the sameconfiguration, Ic0 and Δ were measured, and average values werecalculated. Further, there might be variations in the patterns ofstorage elements, the value of Ic0 was divided by the area of thestorage layer 32, to determine the inversion current density Jc0.

Table 1 shows measurement results for the thermal stability index andthe inversion current density Jc0.

TABLE 1 Spin- Spin-barrier absorption layer layer Cap layer Δ Jc0[MA/cm²] Comparative NA NA Ta(5) 35 6.0 Example 1 Comparative NA Pt(3)Ta(5) 51 13.3 Example 2 Comparative MgO(1.1) NA Ta(5) 45 4.2 Example 3Example 1 MgO(1.1) Pt(3) Ta(5) 47 3.3 Example 2 MgO(1.1) Pd(3) Ta(5) 463.3

NA: not applicable

As shown in Table 1, Comparative Example 1 having the most typicalconfiguration without a spin barrier layer 18 and spin absorption layer19 had the results of Δ=35 and Jc0=6.0 MA/cm2.

Next, Comparative Example 3 having the spin barrier layer 18 but nothaving the spin absorption layer 19 had the results of Δ=45, Jc0=4.2MA/cm2. Thus by providing a spin barrier layer 18, thermal stability isimproved and moreover the inversion current is reduced, and so theconfiguration may be suitable for a storage element.

On the other hand, Comparative Example 2, in which a spin barrier layer18 is not provided, but a spin absorption layer 19 of Pt is provideddirectly above the storage layer 32, had the results of Δ=51, Jc0=13.3MA/cm2. Although Δ was further increased, the inversion current wasincreased, to approximately twice the value of Comparative Example 1which indicates a typical configuration, and to approximately threetimes that of Comparative Example 3, which is provided with a spinbarrier layer 18. This is attributed to an increase in the Gilbertdamping constant of the storage layer 32, caused by the fact that thePt, which causes the spin pumping phenomenon, is in direct contact withthe storage layer 32. Since the Ic0 value is increased in such aconfiguration, it is disadvantageous to be used as a storage element.

On the other hand, Examples according to an embodiment include both aspin barrier layer 18 and a spin absorption layer 19. In the case ofExample 1 in which the spin absorption layer 21 was a 3 nm Pt film, theresults were Δ=47 and Jc0=3.3 MA/cm2, whereas in the case of Example 2in which the spin absorption layer 21 was a 3 nm Pd film, the resultswere Δ=46 and Jc0=3.3 MA/cm2.

In other words, in both Examples, whereas Δ was comparable to the valueof Comparative Example 3 in which only a spin barrier layer 18 wasprovided, Jc0 was reduced by approximately 20%. There was no significantdifference between Example 1 and Example 2, and similar advantageousresults were obtained regardless of the spin absorption layer 19 being aPt film or a Pd film.

From the above results, it is shown that when a spin barrier layer 18and spin absorption layer 19 are provided for the storage layer 32, theinversion current density can be reduced, and moreover thermal stabilitycan be improved.

The film configuration of the storage element 3 is not limited to thatdescribed in the above embodiments, and various film configurations canbe employed.

In each of the above-described embodiments, the fixed magnetizationlayer 3 of the storage element has an exchange-bias layeredferrimagnetic structure. However, if magnetization fixing is sufficient,a single-layer ferromagnetic layer may be used, or an antiferromagneticlayer/ferromagnetic layer structure, or a layered ferrimagneticstructure without an antiferromagnetic layer, may be used.

Respective ferromagnetic layers of the fixed magnetization layer are notlimited to single layers, and a layered film including layers ofdifferent materials may be used.

Further, the storage element may be configured to have layers thelayering order of which is opposite to those of the above-describedembodiments.

It should be understood that various changes and modifications to thepresently preferred embodiments described herein will be apparent tothose skilled in the art. Such changes and modifications can be madewithout departing from the spirit and scope of the present subjectmatter and without diminishing its intended advantages. It is thereforeintended that such changes and modifications be covered by the appendedclaims.

The invention is claimed as follows:
 1. A storage element comprising: afirst magnetization layer having a first magnetization state; a secondmagnetization layer having a second magnetization state; an intermediatelayer provided between the first magnetization layer and the secondmagnetization layer; a third layer including at least one of Pt, Ru, Pdand Au; and a fourth layer including at least one of an oxide, a nitrideand a fluoride, wherein the second magnetization layer includes at leasta first sublayer having a first magnetization direction and a secondsublayer having a second magnetization direction, and wherein the fourthlayer is provided between the third layer and the first magnetizationlayer.
 2. The storage element according to claim 1, wherein each of thefirst sublayer and the second sublayer includes a material having anelement selected from a group consisting of Fe, Ni and Co.
 3. Thestorage element according to claim 1, wherein the second magnetizationlayer further includes a non-magnetic layer provided between the firstsublayer and the second sublayer.
 4. The storage element according toclaim 3, wherein the non-magnetic layer includes Ru.
 5. The storageelement according to claim 4, wherein the non-magnetic layer has athickness from 0.5 to 2.5 nm.
 6. The storage element according to claim1, wherein the storage element further includes an underlayer, and theunderlayer includes Ta.
 7. The storage element according to claim 1,wherein the storage element further includes a cap layer, and the caplayer includes Ta.
 8. The storage element according to claim 1, whereinthe second magnetization layer includes an alloy comprising nickel. 9.The storage element according to claim 8, wherein the alloy furthercomprises Cr.
 10. The storage element according to claim 1, wherein theintermediate layer includes at least one of magnesium oxide, aluminumoxide, aluminum nitride, SiO₂, Bi₂O₃, MgF₂, CaF, SrTiO₂, AlLaO₃, andAlNO.
 11. The storage element according to claim 10, wherein theintermediate layer has a thickness of 1.5 nm or less.
 12. The storageelement according to claim 10, wherein the intermediate layer has athickness of approximately 0.8 nm.
 13. The storage element according toclaim 1, wherein the second magnetization layer has a thickness from 1nm to 40 nm.
 14. The storage element according to claim 1, wherein thefirst magnetization layer has a thickness from 1 nm to 10 nm.
 15. Thestorage element according to claim 14, wherein the first magnetizationlayer has a thickness less than 5 nm.
 16. The storage element accordingto claim 15, wherein the first magnetization layer has a thickness ofapproximately 2.2 nm.
 17. The storage element according to claim 1,wherein the second magnetization layer is thicker than the firstmagnetization layer.
 18. The storage element according to claim 17,wherein the first sublayer is between the intermediate layer and thesecond sublayer, and the second sublayer is thicker than the firstsublayer.
 19. The storage element according to claim 18, wherein thefirst sublayer is thicker than the first magnetization layer.
 20. Thestorage element according to claim 1, wherein the first sublayer isbetween the intermediate layer and the second sublayer, and the firstsublayer has a thickness from 1 nm to 5 nm.
 21. The storage elementaccording to claim 1, wherein the third layer is thicker than the fourthlayer.
 22. The storage element according to claim 1, wherein each of thefirst sublayer and the second sublayer are thicker than each of thethird layer and the fourth layer.
 23. The storage element according toclaim 1, wherein the first magnetization layer includes Co, Fe, and B.24. A memory comprising: a storage element; and two lines that intersectwith each other, wherein the storage element includes a firstmagnetization layer having a first magnetization state; a secondmagnetization layer having a second magnetization state; an intermediatelayer provided between the first magnetization layer and the secondmagnetization layer; a third layer including at least one of Pt, Ru, Pdand Au; and a fourth layer including at least one of an oxide, a nitrideand a fluoride, wherein the second magnetization layer includes at leasta first sublayer having a first magnetization direction and a secondsublayer having a second magnetization direction, and wherein the fourthlayer is provided between the third layer and the first magnetizationlayer.